Glasgow Haskell is a changing system so there are sure to be
bugs in it.

To report a bug, either:

Go to the SoureForge GHC
page, go to the "bugs" section, click on
"submit", and enter your bug report. You can also
check the outstanding bugs here and search the archives to make
sure it hasn't already been reported. Or:

Take a look at the FAQ (Chapter 13) and Chapter 9, which will give you some guidance as to
whether the behaviour you're seeing is really a bug or
not.

If it is a bug, then it might have been reported before:
try searching the mailing list archives. The archives don't
have a built-in search facility, but we find that Google's site search works
pretty well: enter
"site:www.haskell.org" followed
by your search term into Google.